In the prior art and more particularly in Belgium Pat. Nos. 832921 and 855153 the class of compounds thiazolo[5,4-c]rifamycins are described which bear a hydrogen atom on the 2 bond-positioned carbon atom of the thiazole ring (i.e. rifamycin P). While the former patent describes the novel compound and a method for producing it by fermenting Nocardia mediterranea strains ATCC 31064, 31065 and 31066, the latter relates to a process for preparing rifamycin P and rifamycin Q, the corresponding 2'-hydroxymethyl derivative, by condensing rifamycin S with a cysteine ester and then decarboxylating or reducing the obtained intermediate. Moreover, some condensation products of rifamycin S with cysteine esters, amides or hydrazides, i.e. thiazolorifamycins characterized by a carbalkoxy, carbamyl or hydrazinocarbonyl group on the 2'-positioned carbon atom, are known from German Offenlegungsschrift No. 2720113.